make a query execution traverser

[andykais]

the ordered scraper query is fairly complex, and debugging it can be difficult. An idea springs to mind where we add some debug blocks to the scraper and then can choose to output the query plan. Things in the debug blocks:

• the ordering info (recurseDepth, horizontalIndex, etc.)
• not the WHERE recurseDepth = {{ lowestDepth }}

somehow we plug this in. Maybe a flag on params and a wrapper on the query statement that consumes the output, then plays it back at 1 second intervals to show how the data moves at each step in the recursion.